Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming, and ultimately very expensive endeavors. As a result, over the years, a significant amount of added emphasis has been placed on well monitoring and maintenance. By the same token, perhaps even more emphasis has been directed at initial well architecture and design. All in all, careful attention to design, monitoring and maintenance may help maximize production and extend well life. Thus, a substantial return on the investment in the completed well may be better ensured.
In the case of well design, architecture and subsequent maintenance, there is often the need to isolate high pressure regions of a cased or lined well with a packer assembly which anchors in place and seals off a region of the well. For example, isolation for the sake of targeted production from a particular region of a well is quite common. However, as well depths continue to become greater and greater, so do well pressures. Thus, the likelihood exists that the well may exceed 20,000 feet in depth, for example, with an architecture targeting an isolated region for production that exceeds 10,000-15,000 PSI. By the same token, a host of interventional applications may also be undertaken which have the effect of introducing such dramatically high pressures in a well. For example, perforations may be formed into the wall of the well at a given location by way of a perforating application which involves isolating the location with a packer assembly. Thus, the packer assembly is subjected to such high pressures introduced by way of the adjacent explosive perforating application.
Faced with such dramatically high pressures, packer assemblies utilize slips to engage and anchor at the wall of the well with a substantial amount of force. For example, the slips may include cast iron teeth which forcibly extended outward into an anchoring biting engagement with the tubular defining the well (i.e. the casing or liner). While generally well suited for anchoring the packer for sake of isolation, the slips may pose a challenge to subsequent applications and interventions. For example, where the packer is utilized for a temporary isolation such as in perforating, there is a subsequent need to remove the packer in advance of production. However, relatively large anchoring slips of cast iron may be a challenge to remove for sake of subsequent production.
A mechanical packer utilizing slips for sake of isolation as described above is generally removed following the isolation application by way of a drill-out or milling application. As noted, this may be a challenge in terms of getting all of the cast iron slip features removed. Indeed, removal of a fully cast iron slip may take well over an hour. Once more, due to the robust nature and high specific gravity of the cast iron material, milling often results in the tool becoming stuck or the material failing to be fully removed. Failure to more fully remove the cast iron material may result in its unintended retrieval during production, potentially harming surface equipment. Potentially even worse though, if the milling tool becomes stuck, all oilfield operations may need to be shut down, followed by time-consuming fishing and/or workover efforts to remediate the situation.
With the above challenges and consequences in mind, efforts have been undertaken to reduce the amount of cast iron or other similarly robust, heavy materials in the slip components of an isolation packer. For example, packers now often reserve the cast iron-type of materials for the teeth or “wicker” portion of the slip while utilizing aluminum for underlying slip components such as the slip ring and base. By way of comparison, an aluminum base material would have a specific gravity of under about 3, whereas cast-iron based materials have a specific gravity that is between about 7 and 8. Therefore, the time required to mill out the plug may be substantially reduced, for example, taking closer to about 30 minutes than say an hour or more which is likely if the slip is fully cast iron. Once more, the odds of the milling tool becoming stuck during the removal application are also dramatically reduced.
With this type of thinking in mind, efforts have also been undertaken to replace underlying aluminum components with even lighter polymer composite materials. That is, while the opportunity may not be available to make the teeth of the slip even lighter due to the casing biting requirements, opportunities to make the underlying components lighter and lighter may be available. Indeed, many slips today incorporate such lighter composite materials with specific gravities below about 2. Thus, milling time for such a plug removal may be even further reduced, for example to perhaps less than about 15 minutes depending on the surrounding circumstances.
Unfortunately, utilizing less structurally robust materials for underlying slip components has its drawbacks. That is, while more readily millable after the isolation application, new challenges may be presented in terms of reliably deploying and anchoring the packer for the isolation application itself. For example, once positioned downhole, the slips are configured to shear away from one another and anchor to a casing as a result of the breaking up of the underlying ring or similar feature. However, when considering that the packer is a large piece of equipment being lowered potentially several thousand feet into a well, there is a strong possibility that a composite polymer ring will prematurely break. When this occurs, the packer may become anchored at the wrong location in the well. Not only is this ineffective for the sought isolation but it will require a separate application run to retrieve the packer and start over. Alternatively, there is also the possibility that the packer does not prematurely begin to set but nevertheless does not uniformly shear as intended, again due to the less robust ring being utilized. In this case, the isolation may be compromised due to a less reliable anchoring. Thus, as a practical matter, operators are often left utilizing the less desirable aluminum or even cast iron components from a milling perspective due to the less reliable composite components from an isolation perspective.